Abstract

Sexual communication in plethodontid salamanders is mediated by a proteinaceous pheromone that a male delivers to a female during courtship, boosting her receptivity. The pheromone consists of three proteins from three unrelated protein families. These proteins are among a small group of pheromones known to affect female receptivity in vertebrates. Previously, we showed that the genes of two of these proteins (PRF and SPF) are prone to incessant evolution driven by positive selection, presumably as a consequence of coevolution with female receptors. In this report, we focus on the evolution of the third pheromone protein gene family, plethodontid modulating factor (PMF), to determine whether it shows the same pattern of diversification. We used RT-PCR in mental gland cDNA to survey PMF sequences from three genera of plethodontid salamanders (27 spp.) to measure rates of evolution, level of gene diversification, modes of selection, and types of amino acid substitution. Like PRF and SPF, PMF is produced by a multigene family characterized by gene duplication and high levels of polymorphism. PMF evolution is rapid, incessant, and driven by positive selection. PMF is more extreme in these dimensions than both PRF and SPF. Nestled within this extraordinary variation, however, is a signature of purifying selection, acting to preserve important structural and biochemical features of the PMF protein (i.e., secretion signal, cysteine residues, and pI). Although a pattern of persistent diversification exists at the molecular level, the morphological and behavioral aspects of the pheromone delivery system show evolutionary stasis over millions of years.

Notes

Acknowledgments

We are grateful to R. Feldhoff, P. Wheeler-Feldhoff, and other members of our research team (http://plethodon.science.oregonstate.edu/index.htm) for discussion and help with all phases of this project. We would like to extend our appreciation to R. Highton and M. Westphal for their assistance in the field and with tissue samples. This research was supported by NSF predoctoral Fellowship to CAP and by NSF grants IBN-0110666 and IOS-0818554 to LDH and SJA and IOS-0818649 R. Feldhoff. The sequences reported in this manuscript have been deposited in GenBank under the accession numbers DQ882251–DQ882291 and DQ882379–DQ882569.

Supplementary material

References

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